Time Math Your Phone Calculator Can’t Do
Adding 2:35 and 3:45 isn’t 5:80 — it’s 6:20, because time rolls over at 60, not 100. That quirk makes time arithmetic error-prone by hand and impossible on a standard calculator. This free time calculator adds and subtracts hours, minutes and seconds correctly, and shows the answer as H:M:S, decimal hours, total minutes and total seconds.
Perfect for timesheets, billing, workout totals and project tracking. No signup, everything runs privately in your browser.
Add · Subtract durations
Result
Great for timesheets, billing and workout totals. A negative result simply means the second duration was longer — shown with a minus sign, e.g. −2:00:00.
How to Use the Time Calculator
- Enter the first duration in hours, minutes and seconds.
- Choose + or −, then enter the second duration.
- Read the result in H:M:S plus decimal hours (for payroll), total minutes and total seconds — with the working shown.
How Time Arithmetic Works
Step 2: add or subtract
Step 3: convert back: hours = ÷3600, minutes = remainder ÷60
Worked example (add): 2:35 + 3:45. In seconds: 9,300 + 13,500 = 22,800. Back to H:M:S: 22,800 ÷ 3,600 = 6:20:00 (6.33 decimal hours).
Worked example (subtract): 8:30 − 0:45. In seconds: 30,600 − 2,700 = 27,900 = 7:45:00.
Decimal Hours Reference
| Minutes | Decimal hours | Minutes | Decimal hours |
|---|---|---|---|
| 5 | 0.08 | 35 | 0.58 |
| 10 | 0.17 | 40 | 0.67 |
| 15 | 0.25 | 45 | 0.75 |
| 20 | 0.33 | 50 | 0.83 |
| 25 | 0.42 | 55 | 0.92 |
| 30 | 0.50 | 60 | 1.00 |
Who Adds Up Time
- Hourly workers & freelancers totaling shifts for timesheets and invoices.
- Payroll & billing converting H:M:S to decimal hours for pay math.
- Athletes adding splits, intervals and training blocks.
- Project managers summing task durations into project totals.
Adding Three or More Durations
The calculator combines two durations at a time, so chain longer lists: add the first two, then add the next duration to that result. Totals can pass 24 hours — adding 23:30 and 2:00 gives 25:30:00, which is one full day plus 1:30. That is deliberate: this tool adds durations, not clock times, so shift totals and project hours never wrap around at midnight and lose a day.
Frequently Asked Questions
How do you add hours and minutes?
Add hours to hours and minutes to minutes; if minutes reach 60+, carry one hour over. Example: 2:35 + 3:45 = 5:80 → carry → 6:20. The calculator does the carrying automatically.
How do you subtract time?
Subtract hours and minutes separately; if minutes go negative, borrow one hour (60 minutes). Example: 8:30 − 0:45 → borrow → 7:45.
What is 1.5 hours in hours and minutes?
1 hour 30 minutes. Multiply the decimal part by 60: 0.5 × 60 = 30. The calculator shows decimal hours alongside H:M:S for exactly this conversion.
How do I calculate hours worked for payroll?
Add up the shift durations here, then use the decimal hours result × hourly rate. 7:45 at $20/hr = 7.75 × 20 = $155.00.
Can the result be negative?
Yes — if the second duration is longer, you get a negative like −2:00:00. That simply means duration two exceeded duration one by two hours.
Why can’t I just use a normal calculator?
Because normal calculators work in base 10 and time works in base 60. Typing 2.35 + 3.45 gives 5.80 — wrong on both the hours and the minutes.
Can I add more than two time values?
Yes — chain them. Add the first two durations, then use the result as the first value and add the third. Repeat for as many durations as you have.
Final Thoughts
Time math is one of those small frictions that compounds — a few botched timesheets a month, a few misbilled hours, and suddenly it matters. Let the calculator carry the sixties.
Try our overtime calculator for pay math.